I am sensitive to low frequency sounds . The thing that seems to work for me is to play thunderstorm sounds, with isolating earphones. Because this sound has a high degree of randomness across the frequency spectrum, and its spectrum varies randomly over short timescales as well, external noise is masked even if it's still audible - because the brain can easily fit it into the thunderstorm pattern, and so doesn't get triggered by it.

Your milage may vary of course